In recent years, there has been an ever increasing industry and legislative drive towards increasing the transfer efficiency of fluid materials sprayed from pressurized spray guns. Transfer efficiency can be defined as the amount of sprayed fluid material, such as paint, that goes onto subject parts as compared to the amount lost to overspray and bounceback. A high transfer efficiency decreases fluid material consumption reduces undesirable deposits on adjacent surfaces, and results in relatively less overspray which improves operator visibility. Importantly, transfer efficiency is a measure of the amount of fluid material dispersed into the ambient air which contributes to environmental pollution.
One class of spray gun uses pressurized air for atomizing liquid material and for shaping the envelope or pattern of the atomized liquid material as it is discharged from a nozzle assembly on the gun. Air atomization spray guns broadly fall into two classes. One type of air atomization spray gun uses a low volume flow of high pressure air (LVHP) for atomization and pattern shaping. The air pressure in such guns may typically be in the 40 psi to 100 psi range. The transfer efficiency associated with such guns, however, are far from optimal. This is due to the relatively high air pressures which produces a high degree of overspray and bounceback.
The other broad type of spray gun which uses pressurized air for atomizing liquid material employs a high volume, low pressure (HVLP) spray approach in order to increase fluid material transfer efficiency. The transfer efficiency of HVLP spray guns is much greater than the LVHP spray guns. HVLP atomization utilizes a high volume of air typically delivered at 10 psi or less to atomize fluid material. It is the large volume of air passing in contact with a fluid material in a suitable nozzle assembly which causes atomization of the fluid material.
Many industries have adopted the HVLP approach, either voluntarily or by legislative mandate. For example, currently the Southern California Air Quality Management District's rules and the EPA's National Emission Standards for Hazardous Air Pollutants require spray gun air atomization pressure to be no greater than 10 psi.
There are many applications where parts and surfaces are located in confined spaces and need to be coated with a fluid material. This is especially the case in the aerospace industry. For example, often painting is required in and around complex structures within aircraft wings and under aircraft skin panels. Another example is where lines or beads of sealant are required to be applied in confined spaces to parts and surfaces, such as fasteners and joints. Due to the spatial constraints, gaining access to the subject parts or surfaces may present a formidable task to the spray gun operator. Often, the operator must apply fluid material to parts which the operator cannot even see. In addition, when working in such confined spaces, it is desirable to mitigate overspray onto adjacent parts such as electronic gear, wiring, and the like.
It is therefore evident that there exists a need in the art for a high volume, low pressure spray gun which facilitates operation in confined spaces while mitigating overspray and bounceback.